So, I've been doing some playing around with numbers and order codes, and to get 3 sections of Soviet Motor rifle (taken to maximum size and composition, so that they can be used in all the different scenarios where variants are required) and a platoon command s, along with 4x BMP-1 mounts and a BRDM-2 scout car comes to ~£70 in 20mm.
This is still (a lot) cheaper than 28mm (where a similar force, albeit with less flexibility in terms of squad composition) comes in at around ~£130... but it isn't as cheap as I had been hoping. Now, that's using resin and metal figures and vehicles. The big savings will come in terms of tanks, and other vehicles which are available as plastic kits or die-cast toys*.
The big problem is that I've been looking at 28mms for so long that I have a, for want of a better phrase, emotional attatchment to them. As an example, I have recollections of drooling over the Sloppy Jaloppy cold wars vehicles when they were first released, and wondering at the time if I would ever get any. I just don't get that for most 20mm - that might be down to the poor illustrations on various sites though, as I do have recollections of regretting stuff being 'in the wrong scale' when having looked at Elhiem & Platoon 20 in the past (and the same goes for most of the stuff mentioned on the Winter of '79 blog spot, especially regarding scenery)
*Ironically, due to their lack of popularity and scarcity of figures, the cheapest military vehicles have to be 1/48ths... it's just there isn't too much variety, and as I say, scare figures.